The oxidation of TiB2 particle-reinforced TiAl intermetallic composites

The oxidation kinetics of TiAl alloys with and without (3, 5, 10 wt.%) TiB2 dispersoids were studied between 1073 and 1273 K in atmospheric air. The inert TiB2 dispersoids effectively increased the oxidation resistance of TiAl alloys. The higher the TiB2 dispersoids content, the more pronounced the effect. The oxide scale formed on TiAl-TiB2 composites was triple-layered, consisting mainly of an outer TiO2 layer, an intermediate Al2O3 layer, and an inner (TiO2 + Al2O3) mixed layer. No B2O3 was observed within the oxide scale because of its high vapor pressure. A thin Ti3Al sublayer and discrete TiN particles were found at the oxide-substrate interface, During the oxidation of TiAl alloys with and without TiB2 dispersoids, titanium ions diffused outwardly to form the outer TiO2 layer, while oxygen ions transported inwardly to form the inner (TiO2 + Al2O3) mixed layer. The increased oxidation resistance by the addition of TiB2 was attributed to the enhanced alumina-forming tendency and thin and dense scale formation.